The present invention relates to a process for treating waste water.
A wide variety of processes and combinations of processes are used for treating waste water such as, for example, chemico-physical methods such as precipitation and flocculation, or adsorptive processes, for example using active carbon, or the removal of harmful substances by biodegradation or oxidation of harmful substances by different methods.
The oxidative treatment of waste water with oxygen-containing gases, using titanium, silicon or zirconium-containing mixed catalysts at high temperatures and under pressure is known (EP 0 257 983 A).
In order to be able to perform waste water treatment under ambient conditions, compounds which form hydroxyl radicals, for example hydrogen peroxide, are used in many cases for the oxidation of harmful substances. Frequently, however, hydrogen peroxide alone is not reactive enough. It has to be activated in an appropriate manner.
UV light may be used, for example, for activation purposes. UV light causes amplified production of hydroxyl radicals from hydrogen peroxide. This hydroxyl radical production is also catalyzed by dissolved iron salts. The combination of hydrogen peroxide and dissolved iron(II) salts is called Fenton's reagent (O. Specht, I. Wurdack, D. Wabner "Mehrstufige Pilotanlage zur oxidativen Abwasserbehandlung nach dem Fenton-Verfahren (H.sub.2 O.sub.2 /Fe-Katalysator), Chemie Ingenieur Technik 9/1995).
However, the use of Fenton's reagent has serious disadvantages (I. Wurdack, C. Hofl, G. Sigl, O. Specht, D. Wabner "Oxidativer Abbau von AOX und CSB in realen Abwassern: Vergleich verschiedener "Advanced Oxidation Processes", 3rd GVC conference "Verfahrenstechnik der Abwasser- und Schlammbehandlung", VDI-Verlag 1996): The reaction proceeds only at a very acid pH values between 2 and 3. Thus, the waste water has to be initially acidified, and then neutralized again after oxidation with Fenton's reagent, before it can be passed into a sewage treatment plant or receiving waters. This results in considerable salting out of the waste water and the production of considerable amounts of a sparingly soluble iron hydroxide precipitate which has to be removed. In addition, there is a high, non-specific, consumption of H.sub.2 O.sub.2 during this reaction.
It is accordingly an object of the invention was to get round the disadvantages of Fenton's reagent mentioned above. Salting out of the waste water should be avoided and the non-specific consumption of H.sub.2 O.sub.2 should be restricted as far as possible.